1. Field of the Invention
The present invention relates to a switching power supply apparatus comprising an over-temperature protection circuit.
2. Description of the Related Art
A switching power supply apparatus comprises heat generating electronic parts such as switching elements in the interior, and radiates generated heat from the electronic parts via a radiator portion to prevent an abnormal temperature rise of the power supply apparatus. Also, a switching power supply apparatus is configured so that an over-temperature protection function acts to stop the operation of the power supply apparatus when the temperature of the power supply apparatus rises to an abnormal level due to an overload or other cause.
In switching power supply apparatuses, the computerization of the control systems has advanced in recent years, and devices such as special-purpose or general-purpose control integrated circuits or microprocessors are being used to control switching power supply apparatuses. In addition, switching power supply apparatuses have been made increasingly more compact and the integration of semiconductor elements for power conversion circuits, which are thermal and noise sources, has advanced so that the concentration of heat sources cannot be avoided. As a result, the over-temperature protection function in a switching power supply apparatus, which operates when the temperature of the power supply apparatus rises to an abnormal level, has become an extremely important element from a power supply performance standpoint.
Generally, the over-temperature protection function is implemented so that a control circuit constituted of the above-described various kinds of control system devices performs a protection operation by outputting a signal such as an operation stop signal according to a temperature detected by a temperature detection element. With this kind of conventional over-temperature protection method depending on a control circuit, when an abnormal temperature rise is detected while the power supply apparatus is operating, the over-temperature protection function usually operates because the control circuit is operating normally.
However, if a problem occurs in the control circuit for some reason, the certainty of the operation of the over-temperature protection is lost, and when the over-temperature protection function does not operate, the temperature of the power supply apparatus may rise until it significantly exceeds the stipulated value and the device is finally damaged. Consequently, it may be a problem that the over-temperature protection function, which operates when the temperature of the power supply apparatus rises to an abnormal level, depends only on an ordinary control circuit.
Switching power supply apparatuses are used as the power supplies of various kinds of electronic or electrical devices. For example, a switching power supply apparatus for lighting a discharge lamp generates a high pulse voltage. The pulse voltage generates electrical and magnetic noise, which may cause misoperation of the control circuit. Consequently, a means for protecting the power supply apparatus against an abnormal temperature rise when a problem occurs in the control circuit is required, considering the safety of the final manufactured product.
An object of the present invention is to provide a switching power supply apparatus equipped with an over-temperature protection circuit that operates appropriately even when a problem occurs in the control circuit.
Another object of the present invention is to provide a switching power supply apparatus equipped with an over-temperature protection circuit that is resistant to the effects of noise.
Still another object of the present invention is to provide a switching power supply apparatus equipped with a highly reliable over-temperature protection circuit that has a simple circuit configuration and operates dependably.
To achieve the above-described objects, a switching power supply apparatus of the present invention comprises an input circuit, a switching conversion circuit, a drive circuit, a control circuit, an output circuit and an over-temperature protection circuit.
The switching conversion circuit comprises a switching element having a control electrode, converts a voltage supplied via the input circuit to switching output and outputs that switching output.
The drive circuit supplies a drive signal to the switching element to turn the switching element on and off. The control circuit supplies a control signal to the drive circuit.
The output circuit is supplied with the switching output, adjusts the switching output to a prescribed output and outputs that prescribed output.
The over-temperature protection circuit comprises a temperature detector and a switch, and is connected to the control electrode of the switching element, and cuts off the drive signal via the switch when the temperature detector detects an abnormal temperature in the switching power supply apparatus.
In the switching power supply apparatus described above, the switching conversion circuit comprises a switching element having a control electrode, converts a voltage supplied via the input circuit to switching output and outputs that switching output, as the switching element is turned on and off according to a drive signal supplied from the drive circuit.
Since the switching output is supplied to the output circuit, which adjusts the switching output to a prescribed output and outputs that prescribed output, the supplied voltage can be adjusted to a prescribed output according to the load connected to the switching power supply apparatus and a suitable output can be supplied for the load.
The control circuit supplies a control signal to the drive circuit. The over-temperature protection circuit comprises a temperature detector and a switch, and is connected to the control electrode of the switching element, and cuts of f the drive signal via the switch when the temperature detector detects an abnormal temperature in the switching power supply apparatus. Therefore, the on-off operation of the switching element is stopped and hence, a further temperature rise in the switching power supply apparatus can be prevented.
In this way, the switching power supply apparatus of the present invention can make the over-temperature protection circuit operate appropriately even when a problem occurs in the control circuit since the drive signal is cut off directly via the switch, not via the control circuit, when the temperature detector detects an abnormal temperature in the switching power supply apparatus.
Also, since the wiring from the temperature detector to the control circuit, which had been required by a conventional over-temperature protection circuit, is unnecessary in the switching power supply apparatus of the present invention, the switching power supply apparatus can be made more compact, and the elimination of the wiring from the temperature detector to the control circuit can reduce the effect of noise that had been impressed on the control circuit via the wiring.
In addition, the over-temperature protection circuit of the switching power supply apparatus of the present invention can be considered a highly reliable over-temperature protection circuit that has a simple circuit configuration and operates dependably because the over-temperature protection circuit comprises the temperature detector and the switch, and the drive signal is cut off directly via the switch, not via the control circuit, when the temperature detector detects an abnormal temperature in the switching power supply apparatus.
Further objects, the configuration, and advantages of the present invention are described in detail with reference to the supplied figures. However, the supplied figures are nothing more than simple examples.